STUTTGART (Reuters) - France has blocked the registration of some new Daimler (DAIGn.DE) Mercedes cars which an EU source said was because of a controversial air conditioning coolant.

French authorities have refused to register Mercedes A-Class, B-Class and SL cars assembled since June 12, even though German authorities have approved them, a Daimler spokesman said.

Usually the approval in France follows on automatically from the German approval.

"We have no explanation for why the registration in France was not yet accepted," the spokesman said.

An EU official familiar with the matter said that France had blocked the registration because the cars contained a coolant that was not permitted in the European Union.

The person added that the French transport ministry had informed the Commission about their plans this week and that the Commission would discuss the matter at their next automotive meeting in mid July.

French government officials did not immediately return calls seeking comment.

Daimler said in September that 1234yf, the only air conditioning coolant on the market that conforms to a new European Union directive on greenhouse gases, could be the primary source for a vehicle fire.

It and rival Volkswagen (VOWG_p.DE) are both developing expensive carbon dioxide-based air conditioning systems in order to avoid what they say is a fire hazard posed by Honeywell (HON.N) and DuPont's (DD.N) new refrigerant HFO-1234yf, which emits poisonous hydrogen fluoride gas when it burns.

Daimler is violating the EU directive by continuing exclusively to use the non-flammable R134a. The German authorities agreed to extend a permit already granted before to predecessor models to the new models.

General Motor's (GM.N) European unit Opel began installing 1234yf-based systems in its Mokka model at the start of the year.

Opel said it had found no evidence in a crash test on its new Mokka SUV that the air conditioning refrigerant could catch fire in a collision and release toxic fumes.